All wheel drive robotic vehicle with steering brake

ABSTRACT

A robotic vehicle may include a first chassis platform including a first wheel assembly, a second chassis platform including a second wheel assembly where the first and second chassis platforms are spaced apart from each other, and a combination linkage operably coupling the first and second chassis platforms. The combination linkage may be operably coupled to the first chassis platform via a first link and is operably coupled to the second chassis platform via a second link. The combination linkage employs at least two different coupling features to operably couple the first and second chassis platforms. The at least two different coupling features include at least any two among a fixed attachment, an attachment that enables rotation about a turning axis, and an attachment that enables pivoting about a pivot axis that is substantially perpendicular to the turning axis.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/532,591 filed Jun. 2, 2017, which is a national phase entry ofinternational Application No. PCT/IB2015/059129 filed Nov. 25, 2015,which claims the benefit of U.S. Provisional Application No. 62/086,498filed on Dec. 2, 2014 and U.S. Provisional Application No. 62/170,735filed on Jun. 4, 2015, the entire contents of each are herebyincorporated herein by reference. Claims the benefit of U.S. ProvisionalApplication No. 62/086,498 filed on Dec. 2, 2014 and U.S. ProvisionalApplication No. 62/170,735 filed on Jun. 4, 2015, the entire contents ofeach are hereby incorporated herein by reference.

TECHNICAL FIELD

Example embodiments generally relate to robotic vehicles and, moreparticularly, relate to a robotic vehicle with a steering brake.

BACKGROUND

Yard maintenance tasks are commonly performed using various tools and/ormachines that are configured for the performance of correspondingspecific tasks. Certain tasks, like grass cutting, are typicallyperformed by lawn mowers. Lawn mowers themselves may have many differentconfigurations to support the needs and budgets of consumers.Walk-behind lawn mowers are typically compact, have comparatively smallengines and are relatively inexpensive. Meanwhile, at the other end ofthe spectrum, riding lawn mowers, such as lawn tractors, can be quitelarge. More recently, robotic mowers and/or remote controlled mowershave also become options for consumers to consider.

Robotic mowers are typically capable of transiting over even and uneventerrain to execute yard maintenance activities relating to mowing. Theymay be programmed to stay within a defined area while performing theirmowing tasks, and may even be configured to perform other tasks in thedefined area. Thus, it may be desirable to expand the capabilities ofrobotic mowers to improve their utility and functionality.

BRIEF SUMMARY OF SOME EXAMPLES

Some example embodiments may therefore provide a robotic vehicle that isstructured and controlled in a manner that achieves superiorperformance. In this regard, the robotic vehicle may have improvedturning capabilities based on both its structure and the controlmechanisms employed on the robotic vehicle.

Some example embodiments may improve the ability of robotic vehicles toprovide utility for garden owners or other operators, specifically byenabling the garden owners to operate such vehicles in a variety ofdifferent, and even challenging environments.

Some example embodiments may provide a robotic vehicle including a firstchassis platform comprising a first wheel assembly, a second chassisplatform comprising a second wheel assembly, the first and secondchassis platforms being spaced apart from each other, a linkage operablycoupled to the first chassis platform and the second chassis platform,such that the linkage is fixed relative to the first chassis platform,and such that the second chassis platform is rotatable relative to thefirst chassis platform, the second chassis platform comprises a turningaxis. The robotic vehicle may also include an electric brake disposedproximate to a turning shaft of the linkage, the electric brake beingselectively applied by processing circuitry to resist turning of thesecond chassis platform about the turning axis and being selectivelyreleased to allow the second chassis platform to turn about the turningaxis.

In another example embodiment, a robotic vehicle is provided whichincludes a first chassis platform comprising a first wheel assembly asecond chassis platform comprising a second wheel assembly, the firstand second chassis platforms being spaced apart from each other, alinkage operably coupled to the first chassis platform and the secondchassis platform, such that the linkage is fixed relative to the firstchassis platform, and such that the second chassis platform is rotatablerelative to the first chassis platform. The second chassis platformcomprises a turning axis. The robotic vehicle may also include anelectropermanent magnet including a brake disc and an electromagnetconfigured to engage the brake disc when applied and disposed proximateto a turning shaft of the linkage, the electric brake being selectivelyapplied by the processing circuitry to resist turning of the secondchassis platform about the turning axis and being selectively releasedto allow the second chassis platform to turn about the turning axis.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

Having thus described the disclosure in general terms, reference willnow be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

FIG. 1 illustrates an example operating environment for a robotic mowerthat may employ an example embodiment;

FIG. 2 illustrates a block diagram of various components of processingcircuitry of the robotic mower to illustrate some of the components thatenable the functional performance of the robotic mower and to facilitatedescription of an example embodiment;

FIG. 3 illustrates a block diagram of various components the roboticmower to facilitate description of some structural components that maybe used to implement an example embodiment;

FIG. 4, which includes FIGS. 4A and 4B, illustrates a perspective viewof the robotic mower in accordance with an example embodiment;

FIG. 5, which includes FIGS. 5A and 5B, illustrates various views of therobotic mower with the first and second housing portions removed to showa turning capability of one example embodiment that has a curvedcombination linkage between chassis platforms;

FIG. 6, which includes FIGS. 6A and 6B, illustrates various views of therobotic mower with the first and second housing portions removed to showa turning capability of one example embodiment that has a straightcombination linkage between chassis platforms;

FIG. 7A illustrates the combination linkage connecting the first chassisplatform to the second chassis platform in accordance with an exampleembodiment;

FIG. 7B illustrates an example combination linkage including twocombination linkage arms according to an example embodiment.

FIG. 8, which includes FIGS. 8A and 8B, shows examples of how pivotingabout the pivot axis allows a common axis of a first wheel assembly anda common axis of a second wheel assembly to be in different planes inaccordance with an example embodiment;

FIG. 9A illustrates a cross section view of the turn assembly tofacilitate a description of how the rotation about the turning axis andpivot axis may be accomplished in accordance with one exampleembodiment;

FIG. 9B illustrates a perspective view of a turn assembly in accordancewith an example embodiment;

FIG. 9C illustrates a perspective view of an electric brake inaccordance with an example embodiment;

FIG. 9D illustrates a diagram of an electric brake in accordance with anexample embodiment;

FIG. 9E illustrates an example electric brake according to an exampleembodiment;

FIG. 9F illustrates an example electric brake according to an exampleembodiment;

FIG. 9G illustrates an example turning motor gear drive according to anexample embodiment;

FIGS. 10A and 10B illustrate cross section views of a portion of thesecond chassis platform of example embodiments, to illustrate how aturning motor may be implemented according to an example embodiment;

FIG. 11, which includes FIGS. 11A and 11B, shows a cross sectional viewof the robotic mower to illustrate some components of an exampleembodiment;

FIG. 12 illustrates a perspective view of the robotic mower with coverportions of the chassis platforms further removed to illustrate somecomponents of an example embodiment;

FIG. 13 illustrates a top view of the robotic mower executing a turn inaccordance with an example embodiment;

FIG. 14 illustrates a conceptual representation of the robotic mower toshow various geometric values that are used in calculations for use inconducting turning operations in accordance with an example embodiment;

FIG. 15 illustrates a conceptual representation of the robotic mower toshow various geometric values that are used in calculations for use inconducting turning operations in accordance with an alternate exampleembodiment;

FIG. 16, which includes FIGS. 16A and 16B, illustrates a relationshipbetween a center of gravity of the robotic mower and a contact linepassing through a point at which each of the lower wheels contacts theground in accordance with an example embodiment;

FIG. 17, which includes FIGS. 17A and 17B, illustrates a frontperspective view of the same situations in FIGS. 16A and 16Brespectively, on a given slope in accordance with an example embodiment;

FIG. 18, which includes FIGS. 18A and 18B, illustrates a frontperspective view of the robotic mower on a larger slope than that shownin FIG. 17, and having wheels turned 90 degrees in FIG. 18A and only 45degrees in FIG. 18B in accordance with an alternate example embodiment;

FIG. 19 illustrates a block diagram of a method for controlling steeringfor a robotic vehicle in accordance with an example embodiment; and

FIG. 20 illustrates a block diagram of a method for enabling control ofthe turning angle of the robotic mower according to an exampleembodiment.

DETAILED DESCRIPTION

Some example embodiments now will be described more fully hereinafterwith reference to the accompanying drawings, in which some, but not allexample embodiments are shown. Indeed, the examples described andpictured herein should not be construed as being limiting as to thescope, applicability or configuration of the present disclosure. Rather,these example embodiments are provided so that this disclosure willsatisfy applicable legal requirements. Like reference numerals refer tolike elements throughout. Furthermore, as used herein, the term “or” isto be interpreted as a logical operator that results in true wheneverone or more of its operands are true. As used herein, operable couplingshould be understood to relate to direct or indirect connection that, ineither case, enables functional interconnection of components that areoperably coupled to each other.

Robotic vehicles, such as robotic mowers, are generally expected to runautonomously over a defined area and perform a function (e.g., mowing).In the simplest of environments, where the area is relatively small andflat, with a somewhat regular shape, the robotic vehicle may be able totraverse the area with ease. However, when designing and buildingrobotic vehicles, such vehicles must be designed for the worst casescenario and not the simplest in order to ensure that the final productcan be successful in the marketplace. Thus, maneuverability in all sortsof environments (e.g., hilly terrain, narrow paths, complex shapedareas, etc.) can be an important feature of such devices.

One aspect of maneuverability that can be helpful for robotic vehiclesconfigured to operate in challenging environments is the ability to makesmall radius turns. Providing a robotic vehicle that can turn at or neara turning angle of about 90 degrees can be a significant advantage.However, whether turning on slopes or sharply, it may be possible totear up grass or even tip the robotic vehicle over in some situations.Thus, simply providing a robotic vehicle with sharp turning capabilitiesis not necessarily the end of the issue. A robotic vehicle with sharpturning capabilities should be controlled in a manner that intelligentlyemploys its capabilities to avoid damaging grass and/or the vehicleitself.

In some instances, such as steep slopes or uneven surfaces the rearchassis and wheels may be unstable, e.g. self steer, if a free bearingin employed. A brake may be used when mower is driving straight forwardor backward, or when the mower is executing a turn. In some examples anelectromagnetic brake, such as an electropermanent magnet, may be used.The electric brake may be released when the mower is changing the turnangle and applied when the turn angle, including straight, is achieved,limiting or preventing unintentional turning of the mower duringoperation.

Example embodiments are therefore described herein to provide variousstructural and control-related design features that can be employed toimprove the capabilities of robotic vehicles (e.g., robotic mowers,mobile sensing devices, watering devices and/or the like) to be expandedand employed in an intelligent manner. Other structures may also beprovided and other functions may also be performed as described ingreater detail below.

FIG. 1 illustrates an example operating environment for a robotic mower10 that may be employed in connection with an example embodiment.However, it should be appreciated that example embodiments may beemployed on numerous other robotic vehicles, so the robotic mower 10should be recognized as merely one example of such a vehicle. Therobotic mower 10 may operate to cut grass on a parcel 20 (i.e., a landlot or garden), the boundary 30 of which may be defined using one ormore physical boundaries (e.g., a fence, wall, curb and/or the like), aboundary wire, programmed location based boundaries or combinationsthereof. When the boundary 30 is a boundary wire, the boundary wire mayemit electrical signals that are detectable by the robotic mower 10 toinform the robotic mower 10 when the boundary 30 of the parcel 20 hasbeen reached.

The robotic mower 10 may be controlled, at least in part, via controlcircuitry 12 located onboard. The control circuitry 12 may include,among other things, a positioning module and a sensor module, which willbe described in greater detail below. Accordingly, the robotic mower 10may utilize the control circuitry 12 to define a path for coverage ofthe parcel 20 in terms of performing a task over specified portions orthe entire parcel 20. In this regard, the positioning module may be usedto guide the robotic mower 10 over the parcel 20 and to ensure that fullcoverage (of at least predetermined portions of the parcel 20) isobtained, while the sensor module may detect objects and/or gather dataregarding the surroundings of the robotic mower 10 while the parcel 20is traversed.

If a sensor module is employed, the sensor module may include a sensorsrelated to positional determination (e.g., a boundary wired detector, aGPS receiver, an accelerometer, a camera, a radar transmitter/detector,an ultrasonic sensor, a laser scanner and/or the like). Thus, forexample, positional determinations may be made using GPS, inertialnavigation, optical flow, radio navigation, visual location (e.g.,VSLAM) and/or other positioning techniques or combinations thereof.Accordingly, the sensors may be used, at least in part, for determiningthe location of the robotic mower 10 relative to boundaries or otherpoints of interest (e.g., a starting point or other key features) of theparcel 20, or determining a position history or track of the roboticmower 10 over time. The sensors may also detect collision, tipping over,or various fault conditions. In some cases, the sensors may also oralternatively collect data regarding various measurable parameters(e.g., moisture, temperature, soil conditions, etc.) associated withparticular locations on the parcel 20. Further, in some cases, thesensors may be used to detect slope and/or traction impacting conditionsalong with the amount of or angle of turn being attempted by the roboticvehicle. As will be discussed below, the robotic mower 10 may beconfigured to control the turn angle based on various factors tooptimize turning capabilities while minimizing any risks associated withengaging in large angle turns in certain conditions or circumstances.

In an example embodiment, the robotic mower 10 may be battery poweredvia one or more rechargeable batteries. Accordingly, the robotic mower10 may be configured to return to a charge station 40 that may belocated at some position on the parcel 20 in order to recharge thebatteries. The batteries may power a drive system and a blade controlsystem of the robotic mower 10. However, the control circuitry 12 of therobotic mower 10 may selectively control the application of power orother control signals to the drive system and/or the blade controlsystem to direct the operation of the drive system and/or blade controlsystem. Accordingly, movement of the robotic mower 10 over the parcel 20may be controlled by the control circuitry 12 in a manner that enablesthe robotic mower 10 to systematically traverse the parcel whileoperating a cutting blade to cut the grass on the parcel 20. In caseswhere the robotic vehicle is not a mower, the control circuitry 12 maybe configured to control another functional or working assembly that mayreplace the blade control system.

In some embodiments, the control circuitry 12 and/or a communicationnode at the charge station 40 may be configured to communicatewirelessly with an electronic device 42 (e.g., a personal computer, acloud based computer, server, mobile telephone, PDA, tablet, smartphone, and/or the like) of a remote operator 44 (or user) via wirelesslinks 46 associated with a wireless communication network 48. Thewireless communication network 48 may provide operable coupling betweenthe remote operator 44 and the robotic mower 10 via the electronicdevice 42, which may act as a remote control device for the roboticmower 10 or may receive data indicative or related to the operation ofthe robotic mower 10. However, it should be appreciated that thewireless communication network 48 may include additional or internalcomponents that facilitate the communication links and protocolsemployed. Thus, some portions of the wireless communication network 48may employ additional components and connections that may be wiredand/or wireless. For example, the charge station 40 may have a wiredconnection to a computer or server that is connected to the wirelesscommunication network 48, which may then wirelessly connect to theelectronic device 42. As another example, the robotic mower 10 maywirelessly connect to the wireless communication network 48 (directly orindirectly) and a wired connection may be established between one ormore servers of the wireless communication network 48 and a PC of theremote operator 44. In some embodiments, the wireless communicationnetwork 48 may be a data network, such as a local area network (LAN), ametropolitan area network (MAN), a wide area network (WAN) (e.g., theInternet), and/or the like, which may couple the robotic mower 10 todevices such as processing elements (e.g., personal computers, servercomputers or the like) or databases. Accordingly, communication betweenthe wireless communication network 48 and the devices or databases(e.g., servers, electronic device 42, control circuitry 12) may beaccomplished by either wireline or wireless communication mechanisms andcorresponding protocols.

FIG. 2 illustrates a block diagram of various components of the controlcircuitry 12 to illustrate some of the components that enable or enhancethe functional performance of the robotic mower 10 and to facilitatedescription of an example embodiment. In some example embodiments, thecontrol circuitry 12 may include or otherwise be in communication with apositioning module 80 and/or a sensor network 90 disposed at the roboticmower 10. As such, for example, the functions attributable to thepositioning module 80 and/or the sensor network 90 may be carried outby, under the control of, or in cooperation with the control circuitry12 in some cases.

The control circuitry 12 may include processing circuitry 110 that maybe configured to perform data processing or control function executionand/or other processing and management services according to an exampleembodiment of the present invention. In some embodiments, the processingcircuitry 110 may be embodied as a chip or chip set. In other words, theprocessing circuitry 110 may comprise one or more physical packages(e.g., chips) including materials, components and/or wires on astructural assembly (e.g., a baseboard). The structural assembly mayprovide physical strength, conservation of size, and/or limitation ofelectrical interaction for component circuitry included thereon. Theprocessing circuitry 110 may therefore, in some cases, be configured toimplement an embodiment of the present invention on a single chip or asa single “system on a chip.” As such, in some cases, a chip or chipsetmay constitute means for performing one or more operations for providingthe functionalities described herein.

In an example embodiment, the processing circuitry 110 may include oneor more instances of a processor 112 and memory 114 that may be incommunication with or otherwise control a device interface 120 and, insome cases, a user interface 130. As such, the processing circuitry 110may be embodied as a circuit chip (e.g., an integrated circuit chip)configured (e.g., with hardware, software or a combination of hardwareand software) to perform operations described herein. However, in someembodiments, the processing circuitry 110 may be embodied as a portionof an on-board computer. In some embodiments, the processing circuitry110 may communicate with electronic components and/or sensors of therobotic mower 10 via a single data bus. As such, the data bus mayconnect to a plurality or all of the switching components, sensorycomponents and/or other electrically controlled components of therobotic mower 10.

The processor 112 may be embodied in a number of different ways. Forexample, the processor 112 may be embodied as various processing meanssuch as one or more of a microprocessor or other processing element, acoprocessor, a controller or various other computing or processingdevices including integrated circuits such as, for example, an ASIC(application specific integrated circuit), an FPGA (field programmablegate array), or the like. In an example embodiment, the processor 112may be configured to execute instructions stored in the memory 114 orotherwise accessible to the processor 112. As such, whether configuredby hardware or by a combination of hardware and software, the processor112 may represent an entity (e.g., physically embodied in circuitry—inthe form of processing circuitry 110) capable of performing operationsaccording to embodiments of the present invention while configuredaccordingly. Thus, for example, when the processor 112 is embodied as anASIC, FPGA or the like, the processor 112 may be specifically configuredhardware for conducting the operations described herein. Alternatively,as another example, when the processor 112 is embodied as an executor ofsoftware instructions, the instructions may specifically configure theprocessor 112 to perform the operations described herein.

In an example embodiment, the processor 112 (or the processing circuitry110) may be embodied as, include or otherwise control the positioningmodule 80, the sensor network 90, and/or other functional components 100of or associated with the robotic mower 10. As such, in someembodiments, the processor 112 (or the processing circuitry 110) may besaid to cause each of the operations described in connection with thepositioning module 80, the sensor network 90, and/or other functionalcomponents 100 by directing the positioning module 80, the sensornetwork 90, and/or other functional components 100, respectively, toundertake the corresponding functionalities responsive to execution ofinstructions or algorithms configuring the processor 112 (or processingcircuitry 110) accordingly. These instructions or algorithms mayconfigure the processing circuitry 110, and thereby also the roboticmower 10, into a tool for performing corresponding functions in thephysical world in accordance with the instructions provided.

In an exemplary embodiment, the memory 114 may include one or morenon-transitory memory devices such as, for example, volatile and/ornon-volatile memory that may be either fixed or removable. The memory114 may be configured to store information, data, applications,instructions or the like for enabling the positioning module 80, thesensor network 90, and/or other functional components 100 to carry outvarious functions in accordance with exemplary embodiments of thepresent invention. For example, the memory 114 could be configured tobuffer input data for processing by the processor 112. Additionally oralternatively, the memory 114 could be configured to store instructionsfor execution by the processor 112. As yet another alternative, thememory 114 may include one or more databases that may store a variety ofdata sets responsive to input from various sensors or components of therobotic mower 10. Among the contents of the memory 114, applications maybe stored for execution by the processor 112 in order to carry out thefunctionality associated with each respective application.

The user interface 130 (if implemented) may be in communication with theprocessing circuitry 110 to receive an indication of a user input at theuser interface 130 and/or to provide an audible, visual, mechanical orother output to the user. As such, the user interface 130 may include,for example, a display, one or more buttons or keys (e.g., functionbuttons), and/or other input/output mechanisms (e.g., microphone,speakers, cursor, joystick, lights and/or the like).

The device interface 120 may include one or more interface mechanismsfor enabling communication with other devices either locally orremotely. In some cases, the device interface 120 may be any means suchas a device or circuitry embodied in either hardware, or a combinationof hardware and software that is configured to receive and/or transmitdata from/to sensors or other components in communication with theprocessing circuitry 110. In some example embodiments, the deviceinterface 120 may provide interfaces for communication of data from thecontrol circuitry 12, the positioning module 80, the sensor network 90,and/or other functional components 100 via wired or wirelesscommunication interfaces in a real-time manner, as a data packagedownloaded after data gathering or in one or more burst transmission ofany kind.

The positioning module 80 may be configured to utilize one or moresensors to determine a location of the robotic mower 10 and directcontinued motion of the robotic mower 10 to achieve appropriate coverageof the parcel 20. As such, the robotic mower 10 (or more specifically,the control circuitry 12) may use the location information to determinea mower track and provide full coverage of the parcel 20 to ensure theentire parcel is mowed. The positioning module 80 may therefore beconfigured to direct movement of the robotic mower 10, including thespeed and direction of the robotic mower 10. Various sensors of sensornetwork 90 the robotic mower 10 may be included as a portion of, orotherwise communicate with, the positioning module 80 to, for example,determine vehicle speed/direction, vehicle location, vehicle orientationand/or the like. Sensors may also be used to determine motor run time,machine work time, and other operational parameters. In someembodiments, positioning and/or orientation sensors (e.g., globalpositioning system (GPS) receiver and/or accelerometer) may be includedto monitor, display and/or record data regarding vehicle position and/ororientation as part of the positioning module 80. In an exampleembodiment, the sensor network 90 may include an angle sensor 190 thatmay be configured to determine the turning angle of the robotic mower 10(or of a set of wheels or individual chassis portion of the roboticmower 10).

The angle sensor 190 may be provided in a number of different forms,some of which will be described in greater detail below. However, insome cases, the angle sensor 190 may be any means such as a device orcircuitry embodied in either hardware, or a combination of hardware andsoftware that is configured to determine a turning angle of one chassisportion or set of wheels relative to another chassis portion or set ofwheels.

FIG. 3 illustrates a block diagram of some of the components of therobotic mower 10 of an example embodiment. In this regard, as shown inFIG. 3, the robotic mower 10 may include a first chassis platform 200and a second chassis platform 210. The first and second chassisplatforms 200 and 210 may be spaced apart from each other and may beoperably coupled to each other via a combination linkage 220. In someembodiments, the first and second chassis platforms 200 and 210 may notcontact each other except as provided by the operable coupling via thecombination linkage 220.

In an example embodiment, the first and second chassis platforms 200 and210 may each support one or more wheels. In cases where each of thefirst and second chassis platforms 200 and 210 supports a correspondingset of two wheels, a first wheel assembly 202 may be provided withindividual wheels on opposite sides of the first chassis platform 200relative to a longitudinal centerline of the robotic mower 10. A secondwheel assembly 212 may be provided with wheels on opposite sides of thesecond chassis platform 210 relative to the longitudinal centerline ofthe robotic mower 10. The wheel bases of the first and second wheelassemblies 202 and 212 could be the same or different. In an exampleembodiment, the wheel bases of the first and second wheel assemblies 202and 212 may be substantially the same as the respective widths of thefirst and second chassis platforms 200 and 210, respectively. Moreover,in some cases, the widths of the first and second chassis platforms 200and 210 may be different such that one such platform has a wider width(and therefore wider wheel base) than the other.

In some example embodiments, each wheel of the first wheel assembly 202may be powered by a single first drive motor (which may be an electricmotor in some examples). Each wheel of the second wheel assembly 212 mayalso be powered by a single second drive motor (which may again be anelectric motor). In such examples, power may be deliverable (selectivelyor continuously) from the respective drive motors to each of the wheelsso that the robotic mower 10 has drive power deliverable to all fourwheels. Thus, the robotic mower 10 may be considered to be an all-wheeldrive (AWD) robotic vehicle.

In an example embodiment, as shown in FIG. 3, each one of the wheels mayhave its own separate drive motor. Thus, each wheel of the first wheelassembly 202 may be powered by a corresponding drive motor of a firstset of drive motors 204 (each of which may be an electric motor). Eachwheel of the second wheel assembly 212 may also be powered by acorresponding drive motor of a second set of drive motors 214 (each ofwhich may again be an electric motor). In such examples, power may bedeliverable (selectively or continuously) from the respective drivemotors to each of the wheels so that the robotic mower 10 has drivepower deliverable to all four wheels to again provide an AWD roboticvehicle. It should be appreciated that each drive motor of the first andsecond sets of drive motors 204 and 214 may be individually controlled(via the control circuitry 12) both for direction of rotation of itsrespective wheel and for speed of turning. Thus, each wheel can beturned in different directions and at different speeds (or the samedirection and same speed) simultaneously. This level of control canenable the control circuitry 12 to intelligently control operation ofthe wheels for optimal turning based on situational factors associatedwith the intended route of the robotic mower 10 and the conditions andterrain on which the robotic mower 10 is located.

As can be appreciated from FIG. 3, the control circuitry 12 and thedrive motors may be powered via a power unit 230. The power unit 230 maybe a rechargeable battery or battery pack that may be supported by oneof the first chassis platform 200 or the second chassis platform 210.Although FIG. 3 shows the power unit 230 and control circuitry 12 on thefirst chassis platform 200, it should be appreciated that the power unit230 and control circuitry 12 may be provided on the second chassisplatform 210 in alternative embodiments. Moreover, in some cases, thepower unit 230 may be distributed on both the first and second chassisplatforms 200 and 210. When power and control are hosted on one of thechassis platforms, wires or other connections to provide power and/orcontrol to components of the other platform may be provided through orproximate to the combination linkage 220 in some cases. In still otherembodiments (see FIG. 12) the power unit 230 and the control circuitry12 may be on opposite ones of the first and second chassis platforms 200and 210.

The combination linkage 220 may be used to operably couple the firstchassis platform 200 to the second chassis platform 210, as describedabove. In some embodiments, the combination linkage 220 may beconfigured to provide a combination of different coupling featureswithin the same structure. The different coupling features may include,for example, a fixed attachment, a non-fixed attachment, an attachmentthat permits rotation about a turning axis, and/or an attachment thatpermits pivoting about a pivot axis that may be substantiallyperpendicular to the turning axis.

As can be appreciated from FIG. 3, the combination linkage 220 may beoperably coupled to the first chassis platform 200 via a first link 222and to the second chassis platform via a second link 224. In an exampleembodiment, the combination linkage 220 may employ at least two of theabove listed coupling features. In this regard, it should be noted thatthe at least two coupling features that are employed could be employedon the same link or on different links. Thus, for example, the firstlink 222 may employ both rotation about a turning axis and pivotingabout a pivot axis substantially perpendicular to the turning axis.Alternatively, for example, the first link 222 may be an attachment thatpermits rotation about a turning axis and the second link 224 may be afixed attachment (i.e., not flexible, but maintaining a fixedorientation between the combination linkage 220 and the second chassisplatform 210 during a turn and during straight ahead operation).

In some embodiments, a turning motor 228 may be powered by the powerunit 230 and controlled by the control circuitry 12 to facilitateturning of the robotic mower 10 as described in greater detail below.However, turning of the robotic mower 10 can be handled entirely bycontrol of speed and direction of turning of the wheels. Thus, theturning motor 228 could be completely eliminated in some embodiments.

FIG. 4, which includes FIGS. 4A and 4B, illustrates a perspective viewof the robotic mower 10 in accordance with one example embodiment. Inthis regard, FIG. 4A shows the robotic mower 10 being steered forstraight ahead driving, while FIG. 4B shows the robotic mower 10executing a turn. In the example of FIG. 4, the robotic mower is shownhaving a first housing 300 covering the first chassis platform 200 and asecond housing 310 covering the second chassis platform 210. Thehousings shown in FIG. 4 are merely exemplary, however, and should notbe seen as being limiting in any way. That said, it may be desirable tokeep the combination linkage 220 covered or out of view, and so thefirst housing 300 is shown in this example to cover over the combinationlinkage 220 and also cover at least a portion of the second housing 310.As such, the first housing 300 may remain fixed in its relationship ororientation relative to the combination linkage 220 (even during aturn), but the second housing 310 may vary its orientation relative tothe first housing 300 and the combination linkage 220 during a turn.

FIGS. 5 and 6 show two different example structures for employing thecombination linkage 220. In this regard, FIG. 5, which includes FIGS. 5Aand 5B, illustrates a top view (FIG. 5A) and a perspective view (FIG.5B) of the robotic mower 10 with the first and second housing portionsremoved. In FIG. 5, the combination linkage 220 is embodied as a curvedmember having a C-shape or U-shape that provides a large clearance toenable either of the wheels of the second wheel assembly 212 to freelypass under the combination linkage 220. Meanwhile, FIG. 6, whichincludes FIGS. 6A and 6B, illustrates a top view (FIG. 6A) and aperspective view (FIG. 6B) of the robotic mower 10 with the first andsecond housing portions removed to show an alternative combinationlinkage 220′ design. In FIG. 6, the combination linkage 220′ is embodiedas a relatively straight member that does not provide clearance toenable either of the wheels of the second wheel assembly 212 to freelypass under the combination linkage 220′. Thus, the turn radius issomewhat limited for this example.

Referring to FIG. 5, the combination linkage 220 of this example has afixed connection to the first chassis platform 200. As such, thecombination linkage 220 extends rearward from the first chassis platform200 toward the second chassis platform 210 along the longitudinalcenterline of the robotic mower 10. The combination linkage 220 remainsfixed in this orientation relative to the first chassis platform 200.Thus, the first link 222 is fixed (referring to FIG. 3). However, theorientation of the combination linkage 220 relative to the secondchassis platform 210 is variable based on the turning status of therobotic mower 10. When the robotic mower 10 is driving straight ahead,each of the wheel assemblies (202 and 212) may receive equal drive powerto each wheel. However, when turning, at least some of the wheels mayreceive drive power unequally (e.g., at differing speeds and/ordirections). When turning, the second chassis platform 210 may thereforebegin to rotate about a turning axis 400. Thus, the second link 224(referring to FIG. 3) comprises an attachment that permits rotationabout the turning axis 400.

As shown in FIG. 5B, the combination linkage 220 has a C-shape orU-shape that may be formed by respective lift arms that are proximate tothe first chassis platform 200 and the second chassis platform 210respectively. The lift arms may extend upward, substantially parallel toeach other and substantially perpendicular to the longitudinalcenterline of the robotic mower 10 (normal to the surface of theground). Meanwhile, a cross-arm may extend between the lift arms to formthe base of the C or U inverted relative to the ground (so the open sideof the C or U shape points downward). The cross-arm may be substantiallyperpendicular to each of the lift arms, and parallel to the ground. Eachwheel of the second wheel assembly 212 may have a diameter that is lessthan the height of the cross-arm relative to the ground. Thus, eachwheel of the second wheel assembly 212 may be enabled to pass underneaththe cross-arm during a turn as shown in FIG. 5B. Thus, for example,either of the wheels of the second wheel assembly 212 may pass betweenthe first chassis platform 200 and the second chassis platform 210. Thisarrangement enables sharp turns (e.g., 90 degree turns) to be achievablevia the robotic mower 10. Moreover, while the common axis of the firstwheel assembly 202 is maintained substantially perpendicular to thelongitudinal centerline of the robotic mower 10, the common axis of thesecond wheel assembly 212 is variable and can move between beingsubstantially perpendicular to the longitudinal centerline of therobotic mower 10 and being substantially parallel to the longitudinalcenterline of the robotic mower 10 (and past these limits in somecases).

When the combination linkage 220′ of FIG. 6 is employed, the secondwheel assembly 212 is not allowed to move completely underneath thecross-arm as described above. Thus, as shown best in FIG. 6A, the commonaxis of the second wheel assembly 212 is still variable, but can onlymove between being substantially perpendicular to the longitudinalcenterline of the robotic mower 10 and being at about a 45 degree anglerelative to the longitudinal centerline of the robotic mower 10 (ineither direction). Thus, the turn radius of the example of FIG. 6 may beslightly less than the turn radius achievable by the example of FIG. 5.

In some example embodiments, the second link 224 may also be configuredto enable pivoting about a pivot axis that is substantiallyperpendicular to the turning axis. FIG. 7 illustrates how the turningaxis and pivot axis are oriented relative to each other in an exampleembodiment. In this regard, FIG. 7A illustrates the combination linkage220 connecting the first chassis platform 200 to the second chassisplatform 210. The combination linkage 220 includes a cross-arm 240, afirst lift arm 242, and a second lift arm 244, that correspond to therespective same components described above. As can be seen in FIG. 7A,the second lift arm 244 couples to a coupling arm 246, which is operablycoupled to a turn assembly 250. The coupling arm 246 may be operablycoupled to the bottom of the turn assembly 250. The turn assembly 250allows the second chassis platform 210 to rotate about the turning axis400, which is substantially perpendicular to the longitudinal centerlineof the robotic mower 10. However, the operably coupling of the couplingarm 246 and the turn assembly 250 further enables the second chassisplatform 210 to pivot about a pivot axis 410 that is substantiallyperpendicular to the turning axis 400.

In an alternative embodiment, depicted in FIG. 7B, the combinationlinkage may include two combination linkage arms 220 a and 220 b. Thecombination linkage arms 220 a, 220 b maybe operably coupled to couplingarm 246, which, in turn, may be operably coupled to the top of the turnassembly 250.

In an example embodiment, the second chassis platform 210 may be enabledto rotate as much as 360 degrees around the turning axis 400. However,the range of motion about the pivot axis 410 may be substantially less.In this regard, in some cases, the amount of pivoting about the pivotaxis 410 may be limited to about +/−5 degrees or a maximum of +/−10degrees side to side. FIG. 8, which includes FIGS. 8A and 8B, showsexamples of how pivoting about the pivot axis 410 allows the common axisof the first wheel assembly 202 and the common axis of the second wheelassembly 212 to be in different planes due to the ability of the secondchassis platform 210 to pivot about the pivot axis 410. This may providefor enhanced terrain following and contact of the first and second wheelassemblies 202 and 212 regardless of terrain. In this regard, adifferential plane angle α may be defined between the common axis of thefirst wheel assembly 202 and the common axis of the second wheelassembly 212.

FIG. 9A illustrates a cross section view of the turn assembly 250 tofacilitate a description of how the rotation about the turning axis 400and pivot axis 410 may be accomplished in accordance with one exampleembodiment. As shown in FIG. 9A, the turn assembly 250 may include theangle sensor 190 (or turning sensor) mounted at the end of a turningshaft extension 420 that extends from a turning shaft 422 that connectsto the coupling arm 246. The turning shaft 422 may be substantiallyperpendicular to the coupling arm 246 and may be substantially parallelto the second lift arm 244. The angle sensor 190 may be configured tomonitor the orientation of the second chassis platform 210 relative tothe first chassis platform 200 and/or the longitudinal centerline of therobotic mower 10 (or the combination linkage 220).

The turning sensor 190 may be provided proximate to a fixed bracket 260inside which an electric brake 262 may be housed. The electric brake 262may be applied to lock the turning shaft 422 and/or the turning shaftextension 420 at a particular turning angle based on informationindicating the current turning angle as determined by the angle sensor190. Thus, for example, when the electric brake 262 is unlocked, thesecond chassis platform 210 may be free to rotate about the turning axis400 to execute turns or insert a turning angle to position the secondchassis platform 210 at a desirable angle or orientation relative to thefirst chassis platform 200. When driving straight or otherwiseattempting to maintain a particular turning angle, the electric brake262 may be applied, e.g., under the control of the control circuitry 12,to prevent further rotation about the turning axis 400. In an exampleembodiment, the control circuitry 12 may compare the current turn angleto a target turn angle. The control circuitry 12 may applies theelectric brake 262 in response to the current turn angle satisfying aturn angle divergence threshold, for example zero or one degreedivergence from the target turn angle. Similarly, the control circuitry12 releases the electric brake 262 in response to the current turn anglefailing to satisfy the turn angle divergence threshold.

The turning shaft 422 may be enabled to pivot about the pivot axis 410due to the turn assembly 250 allowing a certain amount of “play”relative to the pivot axis 410 to accommodate for terrain and slopechanges. In this regard, a bearing assembly 430 (see FIG. 10) may beprovided that allows the turning shaft 422 to move, at least to somedegree, about the pivot axis 410. In particular, the turn assembly 250(and more particularly the bearing assembly 430 thereof) may include apivot bearing housing 270 to house pivot bearings 272 oriented to allowpivoting about the pivot axis 410 and a turn bearing housing 280 tohouse turn bearings 282 disposed along the turning shaft 422 to supportrotational movement of the turning shaft 422. As such, the pivot bearinghousing 270 may be assembled to screw bosses of the turn bearing housing280 to enable the pivot bearing housing 270 to pivot (e.g., about +/−5degrees). The pivot bearing housing 270 and the second chassis platform210 may therefore both be enabled to rotate and pivot responsive tomovement of the second chassis platform 210 over sloped or uneven groundwhile turning or driving straight ahead.

Although in some cases, turning of the second chassis platform 210 couldbe accomplished by individually controlling speed and/or direction ofdrive power provided to at least some of the wheels of the first andsecond wheel assemblies 202 and 212, in some embodiments, the turningangle can be adjusted directly via a separate component (e.g., theturning motor 228).

FIG. 9B illustrates a perspective view of the turn assembly 250 inaccordance with one example embodiment. The electric brake 262 mayinclude an electromagnet 262′ and a brake disc 263. The electromagnet262′ may rotate about the turning axis 400 with the second chassisplatform 210. The brake disc 263 may be stationary relative to theturning axis 400 and extend around the turning axis to at least themaximum turning direction, for example at least 180 degrees.

FIG. 9C illustrates a perspective view of the electric brake and turnassembly in accordance with an example embodiment. The electromagnet262′ may be operably coupled, e.g. riveted, screwed, welded, or thelike, to fixed mount 260. The fixed mount 260 may be operably coupled tothe second chassis platform 210, such that the fixed mount andelectromagnet 262′ may turn in response to the turning of the secondmounting chassis platform. The brake disc 263 may operably coupled to adisc mounting plate 265. The disc mounting plate 265 may be operablecoupled to the pivot 270, such that the disc mounting plate 265 andbrake disc 263 are stationary relative to the turning axis 400.

In one example embodiment, the brake disc 269 may include a guide, suchas a guide rod 269 and aperture 269′. The guide rod 269 may extend fromthe disc mounting plate 265 through the aperture 269′ allowing brakedisc 263 to move toward and away from the electromagnet 262′, whilebeing stationary relative the turning axis 400, as depicted by arrow F1.In some example embodiments, the guide rod 269 penetrates the aperture269′ but does not penetrate the brake plane, e.g. the surface of thebrake disc 263 which faces the electromagnet 262′. The electromagnet262′ may engage the brake disc 263 at any point, e.g. as theelectromagnet moves it may engage the point of the brake disc which ispresently facing the electromagnet.

In an example embodiment, the electric brake 262 is an electropermanentmagnet as discussed below in FIG. 9D. In some example embodiments, theelectric brake 262 is a friction brake. In an instance in which theelectric brake 262 is a friction brake, the electric brake may apply abrake pad to the brake disc 263 generating a frictional force sufficientto limit or prevent unintentional turning of the second chassis platform210. In another example embodiment, the electric brake 262 may be acaliper brake. In an example embodiment in which the electric brake 262is a caliper brake, the caliper may travel on either side of the brakedisc 263 as the electric brake moves about the turning axis 400 with thesecond chassis platform. Actuation of the caliper may be applied by anelectric motor, or servo, applying tension to the caliper which, inturn, applies force to either side of the brake disc 263. The forceapplied to either side of the brake disc 263 may be sufficient to limitor prevent unintentional turning of the second chassis platform 210. Infurther example embodiments, the electric brake 262 may be a solenoidactuated locking pin. In an example embodiment in which the electricbrake 262 is a solenoid actuated locking pin, the brake disc 263 mayhave one or more apertures or recesses. In an instance in which thelocking pin is actuated, the locking pin may engage at least one of theapertures of recesses, thereby limiting or preventing unintentionalturning of the second chassis platform 210. One of ordinary skill in theart would immediately appreciate that electric brakes described hereinare for illustrative purposes and other brakes beyond those disclosedmay be used to provide steering stability in robotic vehicles, such asmowers.

FIG. 9D illustrates a diagram of an electric brake 262 in accordancewith an example embodiment. The electric brake 262 may include aelectromagnet 902 and a brake disc 263. In an example embodiment, theelectromagnet 902 may be an electropermanent magnet. The electromagnet902 may include two plates 906, and a first permanent magnet 908, asecond permanent magnet 910, and a winding 912. The first permanentmagnet 908 may be a material with a relatively low intrinsic coactivity,such as 50 A/m, for example AlNiCo (Alnico). The second permanent magnet910 may be a material with a relatively high intrinsic coercively, suchas 1120 A/m, for example NdFeB (neodymium). The two plates 906 and brakedisc 904 may be a soft magnet, Hiperco. The coil 912 may be wrappedaround one or both permanent magnets 908, 910, and operably coupled to apower supply which may be selectively applied, such as by a solenoidoperably coupled to the control circuitry 12.

The first and second permanent magnets 908, 910 may be oriented, suchthat the north end of each magnet is operably coupled to opposing plate906. The plates 906 may channel the magnetic flux through the brake disc904, causing the brake disc to be pulled and move towards theelectromagnet 902. The magnetic flux channeled through the plates 906and the brake disc 263 may apply a significant magnetic force betweenthe electromagnet 902 and brake disc, for example 50-100 N. The magneticforce may be sufficient to limit or prevent unintentional turning of thesecond chassis platform 210. As described, the electric brake 262 isnormally locked or applied, without a current being applied to thewinding 612.

In an instance in which, the control circuitry 12 determines a change inturn angle is desired, the electric brake 262 may be unlocked orreleased. An electric current may be applied to the winding 912, causingan electromagnetic field to be induced, opposite of the magnetic fieldof the first permanent magnet 908. In an example embodiment, theelectric current may be continuously applied while the break is releasedor may be a pulse. The magnetic field of the first permanent magnet 908may be reversed by the electromagnetic filed of the winding 912, suchthat the north ends of the first and second permanent magnets 908, 910are operably coupled to the same plate 908. The magnetic flux or fieldmay be focused by the plates 906 through the air around theelectromagnet 902. The brake disc 263 may move away from theelectromagnet 902 due to the magnetic force and/or gravitational force,releasing the electric brake 262 and allowing turning of the secondchassis platform about the turning axis 400. In some exampleembodiments, in an instance in which the brake is released, a gap may beprovided between the brake disc 263 and the electromagnet 902 limitingor preventing wear of the brake disc 263 when as the electromagnet 902moves about the turning axis.

In an embodiment in which the first permanent magnet 908 magnetic fieldis reversed by a electromagnetic field pulse induced by an applicationof current to the winding 912 in a first direction, the magnetic fieldof the permanent magnet may be reversed to the first orientation byapplication of current to the winding in a second direction opposite tothe first direction. In an embodiment in which the first permanentmagnet 908 magnetic field is reversed by continued application of anelectromagnetic field induced by a continuous application of current tothe winding 912, the magnetic field of the permanent magnet may bereversed to the first orientation by interrupting application of currentto the winding. The return of the first permanent magnet 908 to anorientation opposite of the second permanent magnet may lock or applythe electric brake 262, causing the magnetic field to engage the brakedisc 263, as discussed above.

Although the operation of the electropermenant magnet was as normallylocked, e.g. locked when deenergized, one of ordinary skill in the artwould immediately understand that the electropermenat magnet may beconfigured to be normally unlocked, e.g. locked when energized.

Additionally or alternatively, friction of a gear box on the turningmotor 228 may be utilized to maintain the turning angle. In some exampleembodiments, the turning motor 228 may be a step motor. Coils of thestep motor may be energized to maintain a position of the step motor andtherefore maintain the turning angle. In an example embodiment, theelectric brake 262 may include a plunge or rod and the brake disc 263may include one or more apertures. The solenoid may be actuated to causethe plunge or rod to penetrate an aperture of the disc brake locking theelectric brake 262.

FIG. 9E illustrates an example electric brake 262 according to anexample embodiment. The electric brake 262 may include a solenoidconfigured to pivot a locking lever 268. The locking lever 268 maypivoted to engage the brake disc 263. Friction between the locking lever268 and the brake disc 263 may maintain the turning angle. In an exampleembodiment, the locking lever 268 and/or the brake disc may include Vgrooves on the engagement surface to increase friction.

FIG. 9F illustrates an example electric brake 262 according to anexample embodiment. The electric brake 262 may include a solenoidconfigured to pivot a locking lever 268 similar to the electric brakediscussed above in reference to FIG. 9E. The locking lever may beconfigure to push or withdraw a plunge or rod from one or more aperturesin the brake disc 263, as discussed in reference to FIG. 9D. In anexample embodiment, the plunge or rod may be returned to a non-actuatedposition by a return spring 267.

FIG. 9G illustrates an example turning motor gear drive according to anexample embodiment. In an alternative embodiment, the turning motor 228and the electric brake 262 may be replaced with a turning motor geardrive. The turning motor gear drive may include an electric drive motor245 and a worm gear assembly 275 configured to turn about the turningaxis 400. The friction of the worm gear assembly 275 may maintain theturning angle set by the electric drive motor 245.

FIG. 10A illustrates a cross section view of a portion of the secondchassis platform 210 of an example embodiment, to illustrate how theturning motor 228 may be implemented in some cases. As shown in FIG. 10,the turning motor 228 may be operably coupled to a gear motor 290 toturn the gear motor 290 responsive to input from the control circuitry12. The gear motor 290 may be operably coupled to a gear assembly 292that is operably coupled to the turning shaft 422. Thus, by operation ofthe turning motor 228, the turning shaft 422 may be positioned or turnedabout the turning axis 400. Moreover, the turning motor 228 may beemployed to turn the turning shaft 422, and the angle sensor 190 maymonitor the turning angle achieved by the operation of the turning motor228. When the desired turning angle is achieved, the angle sensor 190may detect the achieved turning angle and inform the control circuitry12, the control circuitry 12 may then direct the turning motor 228 tostop turning, and may engage the electric brake 262 as described above.Thus, precise turning angles may be achieved and maintained under thecontrol of the control circuitry 12.

FIG. 10B illustrates a cross section view of a portion of the secondchassis platform 210 of an example embodiment, to show how the turnassembly 250 may be implemented in an alternative embodiment, asdescribed in FIG. 7B above. The turn assembly 250 may be substantiallysimilar to the turning assembly discussed above in reference to FIG.9A-10. The turn assembly 250 may be oriented such that the turningsensor 190 is near the bottom of the turn assembly 250 and the turningshaft 422 is near the top of the turn assembly 250. In an exampleembodiment, the turn assembly 250 may be external to the second housing310. The turn assembly 250 may include a cover such as a plastic cover,to protect the turn assembly from impact damage from water or debris.

The coupling arm 246 of the combination linkage 220 may be operablycoupled to the turning shaft 422. The turn assembly 250 may be operablycoupled to a pivot arm 248, which in turn, may be operably coupled tothe second chassis platform 210 via pivot shaft 247. In someembodiments, the pivot arm may include pivot stops 249 to limit thepivot travel of the pivot arm 248.

FIG. 11, which includes FIGS. 11A and 11B, shows a cross sectional viewof the robotic mower 10 with housings attached (FIG. 11A) and with thehousings removed (FIG. 11B) to illustrate some components of an exampleembodiment. FIG. 12 illustrates a perspective view of the robotic mower10 with cover portions of the chassis platforms further removed toillustrate some components of an example embodiment. Referring to FIGS.11 and 12, the first housing 300 and the second housing 310 may each beoperably coupled to the first and second chassis platforms 200 and 210,respectively, via body suspension mounts 500. The first and secondhousing portions 300 and 310 may provide for a desirable aestheticappearance of the robotic mower 10, and also protect internal componentsthereof from weather, impact or other undesirable events. In an exampleembodiment, the turning shaft 422 may be sealed with a rubber bellows toallow for the pivoting movement of the second chassis platform 210. Theturning shaft 422 may also be sealed with a felt sealing material toallow for turning movement of the second chassis platform 210.

The combination linkage 220 is shown as having a fixed connection (e.g.,shown by first link 222) to the first chassis platform 200. However, theturning shaft 422 allows the second chassis platform 210 to rotate (orbe rotated) to a desired angle that can be monitored by the angle sensor190. The electric brake 262 can be employed to lock in a particular ordesired angle (or at least apply a torque to inhibit or resist movementof the turning shaft 422), as described above. In the example of FIG.12, the power unit 230 is provided at the second chassis platform 210.Meanwhile, a cutting unit 510 may be powered by the power unit 230, butsupported at the first chassis platform 200. Drive motors (e.g., firstset of drive motors 204) may be housed proximate to the respectivewheels that they power. The drive motors are also powered by the powerunit 230 and under control from the control circuitry 12. A main board520, which may embody the processing circuitry 12 in some cases, may beprovided at the first chassis platform 200.

The scale of the robotic mower 10 may be adjustable in some cases, dueto the optimal and fundamental nature of the design concepts that someof the examples described herein embody. Thus, for example, the wheelbases and sizes of the first and second chassis platforms 200 and 210may be increased to support the cutting unit 510 and any desirablenumber of cutting blades from one to multiple such blades.

As discussed above, the robotic mower 10 of an example embodiment may beenabled to have a relatively tight turning radius. FIG. 13 illustrates atop view of the robotic mower 10 executing a turn in accordance with anexample embodiment. As shown in FIG. 13, the turning axis 400 definesthe axis about which the second chassis platform 210 rotates relative tothe longitudinal centerline 600 of the robotic mower 10, when therobotic mower 10 executes a turn. When the second chassis platform 210rotates to create a turn, the turn may be executed in the manner shownin FIG. 13. In this regard, due to the sharpness of the turning angledefined by the amount of rotation of the second chassis platform 210about the turning axis 400, the second wheel assembly 212 may define tworespective circular paths for the wheels of the second wheel assembly212. An outer rear wheel turn radius 610 is shown in FIG. 13 along withan inner rear wheel turn radius 620. The outer rear wheel turn radius610 may be considered to define the smallest or tightest turn radius forthe robotic mower 10.

While the second chassis platform 210 follows the outer rear wheel turnradius 610 and the inner rear wheel turn radius 620 as shown, the firstwheel assembly 202 also defines a circular path for the outer wheel ofthe first wheel assembly 202. The inner front wheel of the first wheelassembly 202 generally pivots about the center point of turning 640,which is the center of all the turn radiuses shown in FIG. 13. The outerfront wheel turn radius 630 is shown in FIG. 13 to intersect the turningaxis 400, but this is not necessarily always the case.

As can be appreciated from FIG. 13, the inner rear wheel of the secondwheel assembly 212 is allowed to pass in between the first chassisplatform 200 and the second chassis platform 210 and under thecombination linkage 220 to achieve the relatively tight turn that isshown. When this turn is executed, the common axis 650 of the firstwheel assembly 202 remains substantially perpendicular to thelongitudinal centerline 600 of the robotic mower 10. However, the commonaxis 660 of the second wheel assembly 212 changes due to the rotationabout the turning axis 400.

As indicated above, the control circuitry 12 may sometimes control theprovision of directions to the robotic mower 10 to direct the roboticmower 10 to traverse all or portions of the parcel 20 of FIG. 1. In somecases, the control circuitry 12 may further be involved in providingspecific control instructions to control turning of the robotic mower 10to achieve optimal results. In this regard, when a robotic vehicle (likethe robotic mower 10) is powered by 3 or 4 wheels, the provision ofpower to each of the wheels individually allows for a high level ofcontrol relative to both steering and to maintaining traction on roughor uneven terrain. As can be appreciated from the discussion above, thecenter point of any turn will depend upon the center axes of the wheels.In particular, the location or position of the center point changesdepending on the angle of rotation of the second chassis platform 210,and each wheel follows its own turning radius. Slippage of any one ofthe wheels could tear the grass, thus it may be desirable to try tolimit such slippage. By employing the angle sensor 190, the geometryinvolved in turning of the robotic mower 10 can continuously bemonitored and/or controlled. The speed of the wheels, direction ofturning of the wheels, and/or the turning angle (e.g., via control ofthe turning motor 228) may all be potentially controllable parameters toinfluence turning or optimize turning.

In an example embodiment, the angle sensor 190 may be configured todetect the turning angle and provide an indication of the same to thecontrol circuitry 12. The control circuitry 12 may then interface withthe turning motor 228 and/or the first and second sets of drive motors204 and 214 to regulate speeds and/or angles accordingly. Whencontrolling speeds, the variable wheel speeds may be calculated based ongeometric formulas and the input from the angle sensor 190. When therobotic mower 10 is driving straight forward, all wheels may be drivenat the same speed. However, when a turn is executed based on speedcontrol (e.g., not using the turning motor 228), one or more of thewheels may be operated at different speeds and/or directions.

FIG. 14 illustrates a conceptual representation of the robotic mower toshow various geometric values that are used in calculations for use inconducting turning operations in accordance with an example embodiment.Relative to FIG. 14, the following terms are defined:

-   -   wb_(f)=wheelbase front    -   wb_(r)=wheelbase rear    -   a_(f)=axle length front    -   a_(r)=axle length rear    -   α=angle between vertical (i.e., longitudinal centerline) and        a_(r)    -   β=(π/2)−α

Based on trigonometry, the following equations may be applicablerelative to determining turn radiuses for each wheel:

$\mspace{76mu}{{bc} = {a_{f} + \frac{a_{r}}{\cos\mspace{14mu}\alpha}}}$${ab} = {\left. {{bc}*\tan\mspace{14mu} a}\rightarrow{ab} \right. = {\left. {\left( {a_{f} + \frac{a_{r}}{\cos\mspace{14mu} a}} \right)*\tan\;\beta}\rightarrow{ab} \right. = {\left. {{a_{f}*\tan\mspace{14mu}\beta} + {\frac{a_{r}}{\cos\mspace{14mu} a}*\tan\;\beta}}\rightarrow{ab} \right. = {\left. {{a_{fg}*\tan\mspace{14mu}\beta} + {\frac{a_{r}}{\cos\mspace{14mu}\alpha}*\frac{\sin\mspace{14mu}\beta}{\cos\mspace{14mu}\beta}}}\rightarrow\left. \left( {{{since}\mspace{14mu} a} = {{\frac{\pi}{23} - {\beta\mspace{14mu}{and}\mspace{14mu}{\cos\left( {\frac{\pi}{2} - \theta} \right)}}} = {\sin\mspace{14mu}\theta}}} \right)\rightarrow{ab} \right. \right. = {\left. {{a_{f}*\tan\mspace{14mu}\beta} + {\frac{a_{r}}{\sin\mspace{14mu}\beta}*\frac{\sin\mspace{14mu}\beta}{\cos\mspace{14mu}\beta}}}\rightarrow{ab} \right. = {a_{f}*\tan\frac{a_{r}}{\cos\mspace{14mu}\beta}}}}}}}$$\mspace{76mu}{{ac} = {\frac{bc}{\cos\;\beta} - \frac{a_{r}}{\tan\mspace{14mu}\beta}}}$

When α is not zero, the wheel radiuses may then be determined based on:

${{Left}\mspace{14mu}{front}\mspace{14mu}{wheel}} = {{ab} + {\frac{{wb}_{f}}{2}*{{sgn}(a)}}}$${{Right}\mspace{14mu}{front}\mspace{14mu}{wheel}} = {{ab} - {\frac{{wb}_{f}}{2}*{{sgn}(a)}}}$${{Left}\mspace{14mu}{rear}\mspace{14mu}{wheel}} = {{ac} + {\frac{{wb}_{r}}{2}*{{sgn}(a)}}}$${{Right}\mspace{14mu}{rear}\mspace{14mu}{wheel}} = {{ac} - {\frac{{wb}_{r}}{2}*{{sgn}(a)}}}$

Using the formulas above, when the angle α is zero, each wheel may runat the same speed to achieve straight running. By finding the largestradius of the four, and dividing each wheel with this a ratio is found.Vehicle speed can then be multiplied by the ratio for each wheel to keepthe vehicle traveling with the determined radius. Thus, the calculationsabove may be used to determine speed/direction to employ for sensorcontrolled wheel steering of an AWD robotic vehicle.

When running, the turning angle may be monitored to either maintain orchange the angle between the first chassis platform 200 and secondchassis platform 210. Similarly, forward and rearward movement of eachwheel relative to corresponding impacts on the turning angle may also bemonitored as described above. However, any or all of speed, directionand angle can be monitored and controlled in some cases. FIG. 15illustrates a conceptual representation of the robotic mower to showvarious geometric values that are used in calculations for use inconducting turning operations in accordance with an example embodiment.

In an example embodiment, geometric calculations may be continuouslyperformed by the control circuitry 12 to enable real time control of thesteering of the robotic mower 10. In particular, various staticmeasurements (e.g., axis lengths, wheel radius, etc.) and the turningangle may be monitored along with speed to provide control (via theprocessing circuitry 12) directed to achieve a target speed and targetangle. The difference between the current turning angle and the targetturning angle may be scaled and adjusted to a suitable angular velocity(w_(r)).

Accordingly, calculations for changing the angle between the firstchassis platform 200 and the second chassis platform 210 may beaccomplished using the definitions and equations discussed below. Withinthis context, a change in turning angle (e.g., the angular differencebetween the heading of the first chassis platform 200 (which is fixed asthe longitudinal centerline) and the heading of the second chassisplatform 210 (which is variable and is perpendicular to the common axisof the second wheel assembly)) may be accomplished by rotating thesecond chassis platform 210 around the turning axis 400. The center ofrotation is fixed in position during the rotation. Rotating the rearchassis will move the front chassis according to the calculations below:

-   -   wb_(f)=wheelbase front    -   wb_(r)=wheelbase rear    -   a_(f)=axis length front    -   a_(r)=axis length rear    -   v=angle of the turning axis    -   w_(r)=angular velocity rear        α=angle between {right arrow over (β_(rot))} and {right arrow        over (β_(tot))}        β=angle between {right arrow over (β_(rev))} and {right arrow        over (β_(tot))}

The speeds of the rear wheels are enabled to be calculated from thewheelbase rear value above since the center of rotation is in the middleof that corresponding axis.

${{Left}\mspace{14mu}{rear}\mspace{14mu}{wheel}} = {{- w_{r}}*\frac{{wb}_{r}}{2}}$${{Right}\mspace{14mu}{rear}\mspace{14mu}{wheel}} = {w_{r}*\frac{{wb}_{r}}{2}}$

For calculating the movement of the front wheels, movement of the pointB may first be calculated: |∥B_(tot)∥=ω_(r)*a_(r). The movement can besplit into two orthogonal parts: {right arrow over (B_(tot))}={rightarrow over (B_(rot))}+{right arrow over (B_(rev))} where {right arrowover (B_(rot) )} is a rotation of the front wheel axis and {right arrowover (B_(rev))} is a movement backwards (reversing). Using these terms,front wheel movement can be determined as:

${{Left}\mspace{14mu}{front}\mspace{14mu}{wheel}} = {{- {\beta_{rev}}} + {{\beta_{rot}}*\frac{{wb}_{f}}{2*a_{f}}}}$${{Right}\mspace{14mu}{front}\mspace{14mu}{wheel}} = {{- {\beta_{rev}}} - {{\beta_{rot}}*\frac{{wb}_{f}}{2*a_{f}}}}$${{Projection}\mspace{14mu}{gives}\mspace{14mu}{the}\mspace{14mu}{lengths}\mspace{14mu}{of}}\mspace{14mu}\underset{B_{rot}}{\rightarrow}\mspace{14mu}{{and}\mspace{14mu}\underset{B_{rev}}{\rightarrow}\text{:}}$β_(rev) = β_(tot) * cos (β) β_(rot) = β_(tot) * cos (a) a = v$\beta = {\frac{\pi}{2} - v}$Where

${{Left}\mspace{14mu}{front}\mspace{14mu}{wheel}} = {{{- \omega_{r}}*{\overset{\_}{u}}_{r}*\sin\mspace{14mu} v} + {w_{r}*{\overset{\_}{u}}_{r}*\cos\mspace{14mu} v*\frac{{wb}_{f}}{2*a_{f}}}}$${{Right}\mspace{14mu}{front}\mspace{14mu}{wheel}} = {{{- w_{r}}*{\overset{\_}{u}}_{r}*\sin\mspace{14mu} v} - {w_{r}*{\overset{\_}{u}}_{r}*\cos\mspace{14mu} v*\frac{{wb}_{f}}{2*a_{f}}}}$Which gives:

By inputting measurements such as wb_(f), a_(f), etc., into thesecalculations, the angle between the chassis (v) and the desired angularvelocity of the rear chassis ω_(r) can be determined. A simplificationof the calculations may involve setting ω_(r) equal to 1 for thecalculations, and then scaling the output to a desired angular velocity.By calculating speed for driving each wheel as described above, wheelslip can be avoided or at least the chances of wheel slip can be reducedsignificantly. Accordingly, it may be less likely that any tearing ofgrass occurs.

In some embodiments, while transiting the parcel 20, the robotic mower10 may encounter slopes of various degrees. Given the small turningradius that the robotic mower 10 is capable of achieving, the risk ofrolling the robotic mower 10 over may increase on certain slopes if awaist angle is greater than 90 degrees. In this regard, the risk ofrolling over may depend at least in part on the relationship between thecenter of gravity of the robotic mower and the amount of the slope.

FIG. 16, which includes FIGS. 16A and 16B, illustrates a relationshipbetween a center of gravity 700 and a contact line passing through thepoint at which each of the lower (in elevation) wheels contacts theground. This point, referred to as intersection point 710, changes whenthe wheels are oriented with different turning angles. In FIG. 16A, atop view of the robotic mower 10 is shown with the contact line 720 alsobeing shown relative to the center of gravity. In the example of FIG.16A, the intersection point 710 is farther away from the center ofgravity 700 since the wheels are all oriented for straight aheaddriving. However, when the wheels of the second chassis platform 210 areturned 90 degrees as shown in FIG. 16B, the contact line 710 and theintersection point 720 are drawn closer to the center of gravity 700.Where there is no slope, neither of these orientations provides arollover risk. However, if the slope increases, this may change.

FIG. 17, which includes FIGS. 17A and 17B, illustrates a frontperspective view of the same situations in FIGS. 16A and 16Brespectively, except on a given slope. FIG. 18, which includes FIGS. 18Aand 18B, illustrates a front perspective view of the robotic mower 10 ona larger slope than that shown in FIG. 17, and having wheels turned 90degrees in FIG. 18A and only 45 degrees in FIG. 18B. It should beunderstood that in the context of FIGS. 16-18, whenever the intersectionpoint 720 remains outside (or right in this view) of the center ofgravity 700, the robotic mower 10 will have a low rollover risk. Anoffset value may therefore be defined and represented by the distanceD_(off) in FIGS. 17 and 18. As can be appreciated from the example ofFIG. 17, the magnitude of D_(off) is larger in FIG. 17A than it is inFIG. 17B. Meanwhile, in the example of FIG. 18A, D_(off) is actually anegative value since the intersection point 720 has moved inside (orleft in this view) of the center of gravity 700. Thus, the rollover riskis high in FIG. 18A. However, on the same slope, by reducing the turningangle to 45 degrees instead of 90 degrees, D_(off) is returned to apositive value, and the rollover risk is again reduced. Accordingly, bymonitoring the slope on which the robotic mower 10 is operating, it maybe possible to control the turning angle to ensure that smaller turningangles are used on larger slopes so that the risk of rollover can bemaintained at low levels. In an example embodiment, the sensor network90 may include an accelerometer that may be configured to determine theorientation of the robotic mower 10 so that the slope on which therobotic mower 10 is operating can be determined. After the slope isdetermined, the control circuitry 12 may impose turning angle limits toprevent rollover.

The waist angle may be defined as the angle between a line along ahorizontal plane pointing into the sloped terrain and a line extendingfrom the intersection point 720 and the center of gravity 700. Thus, itcan be appreciated that the waist angle is less than 90 degrees in FIGS.17A, 17B, and 18B, but is greater than 90 degrees in FIG. 18A.

Embodiments of the present invention at it relates to steering controlmay therefore be practiced using an apparatus such as the one depictedin FIGS. 2-3, in connection with the system of FIG. 1. As such, itshould also be appreciated that some embodiments may be practiced inconnection with a computer program product for performing embodiments oraspects of the present invention by controlling execution of one or moremethods associated with performing example embodiments. FIGS. 19 and 20each illustrate a block diagram of an example method for controllingoperation of the robotic mower in accordance with an example embodiment.Each block or step of the flowcharts of FIGS. 19 and 20, andcombinations of blocks in the flowcharts, may be implemented by variousmeans, such as hardware, firmware, processor, circuitry and/or anotherdevice associated with execution of software including one or morecomputer program instructions. Thus, for example, one or more of theprocedures described herein may be embodied by computer programinstructions, which may embody the procedures described above and may bestored by a storage device (e.g., memory 114) and executed by processingcircuitry 110 (e.g., including by processor 112).

As will be appreciated, any such stored computer program instructionsmay be loaded onto a computer or other programmable apparatus (i.e.,hardware) to produce a machine, such that the instructions which executeon the computer or other programmable apparatus implement the functionsspecified in the flowchart block(s) or step(s). These computer programinstructions may also be stored in a computer-readable medium comprisingmemory that may direct a computer or other programmable apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstructions to implement the function specified in the flowchartblock(s) or step(s). The computer program instructions may also beloaded onto a computer or other programmable apparatus to cause a seriesof operational steps to be performed on the computer or otherprogrammable apparatus to produce a computer-implemented process suchthat the instructions which execute on the computer or otherprogrammable apparatus provide steps for implementing the functionsspecified in the flowchart block(s) or step(s). In this regard, a methodaccording to example embodiments of the invention may include any or allof the operations shown in FIG. 19 or 20. Moreover, other methodsderived from the descriptions provided herein may also be performedresponsive to execution of steps associated with such methods by acomputer programmed to be transformed into a machine specificallyconfigured to perform such methods.

In an example embodiment, a method for providing steering control of arobotic vehicle may include receiving an indication of a target turningangle at operation 800. The target turning angle may be generated basedon turns required to follow a programmed route, instructions receivedfrom a steering algorithm, remotely provided instructions, and/or thelike. An indication of the current turning angle may then be received atoperation 802. The current turning angle may be provided (e.g., by theangle sensor 190) continuously, periodically, or in response to variousevents. Upon receiving the target turning angle and the current turningangle, a determination may be made at operation 804 as to whether thereis a difference between the two. If there is no difference, in somecases the electric brake may then be applied to lock in the currentturning angle at operation 806. If there is a difference, then theelectric brake may be released at operation 808.

A turning angle modification may then be calculated at operation 810.The turning angle modification may be calculated, at least in part,based on the calculations discussed above in connection with thedescription of examples corresponding to FIGS. 14 and 15. As such, forexample, the turning angle modification may include the determination ofan optimal speed/direction modification and/or turning motor input toachieve the desired turning angle to conduct the turn needed to followthe programmed route, received instructions or steering algorithm input.

In some cases, information indicative of the current inclination mayalso be received at operation 812. A comparison may then be made todetermine whether the current inclination exceeds a predefined thresholdinclination at operation 814. If the current inclination is below thethreshold inclination, then the turning angle may be controlled based onthe calculated turning angle modification at operation 816. If thecurrent inclination is above the threshold inclination, then a limit maybe applied to the turning angle modification at operation 818.Regardless of whether a limit needs to be applied, flow may proceed toimplementation of steering control based on the calculated (and/orlimited) turning angle modification at operation 820.

The implementation of steering control may be accomplished in a numberof ways. FIG. 20 illustrates an example of one such way in which suchsteering control may be achieved. In the example of FIG. 20. In somecases, an indication may be provided regarding the calculated (orlimited) turning angle modification at operation 822 and a determinationmay be made as to whether the turn will be conducted with the aid of theturning motor at operation 824. If assistance from the turning motor isnot to be used, then calculations may be made (e.g., involving thecalculations discussed above in connection with the description ofexamples corresponding to FIGS. 14 and 15) to determine what speedand/or direction to employ for the wheels to conduct speed based turningat operation 826. The calculated speeds/directions may then be employeduntil the current turning angle reaches the target turning angle atoperation 828. Of course, if no turning motor is employed at all, themethod may simply skip operation 824 and proceed directly to operation826.

If turning motor assistance is to be employed, then power may be appliedto the turning motor to start implementing a turning angle (as describedabove) at operation 830. If it is possible to combine speed control withturning motor operation, then a determination may be made as to whetherto combine both at operation 832. If the combination will not beemployed, then power may be applied to the turning motor until thecurrent turning angle reaches the target turning angle at operation 834.In examples in which turning is done exclusively with the turning motor,operations 822, 830 and 834 may simply be executed in order.

If both speed control and turning motor operation are desired andpossible, then speed control calculations may be performed at operation836 after operation 832. Thereafter, both speed/direction control andturning motor operation may be applied until the current turning anglereaches the target turning angle at operation 838.

In an example embodiment, an apparatus for performing the methods ofFIGS. 19 and 20 above may comprise processing circuitry (e.g.,processing circuitry 110) that may include a processor (e.g., processor112) configured to perform some or each of the operations (800-838)described above. The processing circuitry 360 may, for example, beconfigured to perform the operations (800-838) by performing hardwareimplemented logical functions, executing stored instructions, orexecuting algorithms for performing each of the operations.Alternatively, the apparatus may comprise means for performing each ofthe operations described above. In this regard, according to an exampleembodiment, examples of means for performing operations (800-838) maycomprise, for example, the processing circuitry 110.

In some embodiments, the features described above may be augmented ormodified, or additional features may be added. These augmentations,modifications and additions may be optional and may be provided in anycombination. Thus, although some example modifications, augmentationsand additions are listed below, it should be appreciated that any of themodifications, augmentations and additions could be implementedindividually or in combination with one or more, or even all of theother modifications, augmentations and additions that are listed. Assuch, in an example embodiment, the robotic vehicle may also include anangle sensor mounted proximate to the turning axis to monitor a turningangle of the second chassis platform relative to the first chassisplatform, the angle sensor providing information indicative of theturning angle to the processing circuitry to enable the processingcircuitry to employ a steering control based on the turning angle. Insome example embodiments, of the robotic vehicle, the processingcircuitry compares a current turn angle to a target turn angle and theprocessing circuitry applies the electric brake in response to thecurrent turn angle satisfying a turn angle divergence threshold and theprocessing circuitry releases the electric brake in response to thecurrent turn angle failing to satisfy the turn angle divergencethreshold. In an example embodiment, the robotic vehicle also includes aturning motor configured to interface with a turning shaft of thelinkage to apply a rotational force to the turning shaft to turn thesecond chassis platform relative to the first chassis platformresponsive to control from the processing circuitry and the processingcircuitry is configured to release an electric brake prior to applyingthe rotational force and apply the electric brake whenever therotational force is not applied.

In some example embodiments of the robotic vehicle the electric brake isdeenergized when applied and energized when released. In an exampleembodiment of the robotic vehicle, the electric brake includes a brakedisc and an electromagnet configured to engage the brake disc whenapplied. In some example embodiments, of the robotic vehicle, the brakedisc and electromagnet comprise an electropermanent magnet. In anexample embodiment of the robotic vehicle, the brake disc is a softmagnet. In some example embodiments of the robotic vehicle, in responseto the electromagnet being energized a magnetic field is reversed. In anexample embodiment of the robotic vehicle, the brake disk is physicallyconnected to a guide rod allowing the brake disc to travel in responseto the application of the electric brake, toward the electric brake, andin response to the release of the electric break, away from the electricbrake. In some example embodiments of the robotic vehicle, the guide rodpenetrates the break disc but does not penetrate a plane in which asurface facing the electromagnet lies. In an example embodiment of therobotic vehicle, the electromagnet is configured to rotate about theturning axis responsive to the second chassis platform turning about theturning axis and the electric brake is stationary relative to theturning axis and the electromagnet aligns with different points of thebrake disc at different points of rotations about the turning axis.

In some example embodiments of the robotic vehicle, the brake discextends around the turning axis to at least a maximum turning angle ofthe second chassis platform. In an example embodiment of the roboticvehicle, the brake disc extends at least 180 degrees around the turningaxis. In some example embodiments of the robotic vehicle, the brake discis forced to a first position in response to the electric brake beingapplied and moves to a second position in response to the electric brakebeing released.

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseinventions pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the inventions are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Moreover, although the foregoing descriptions and the associateddrawings describe exemplary embodiments in the context of certainexemplary combinations of elements and/or functions, it should beappreciated that different combinations of elements and/or functions maybe provided by alternative embodiments without departing from the scopeof the appended claims. In this regard, for example, differentcombinations of elements and/or functions than those explicitlydescribed above are also contemplated as may be set forth in some of theappended claims. In cases where advantages, benefits or solutions toproblems are described herein, it should be appreciated that suchadvantages, benefits and/or solutions may be applicable to some exampleembodiments, but not necessarily all example embodiments. Thus, anyadvantages, benefits or solutions described herein should not be thoughtof as being critical, required or essential to all embodiments or tothat which is claimed herein. Although specific terms are employedherein, they are used in a generic and descriptive sense only and notfor purposes of limitation.

That which is claimed:
 1. A robotic lawn mower comprising: a firstchassis platform comprising a first wheel assembly; a second chassisplatform comprising a second wheel assembly, the first and secondchassis platforms being spaced apart from each other; and a combinationlinkage operably coupling the first and second chassis platforms,wherein the combination linkage is operably coupled to the first chassisplatform via a first link and is operably coupled to the second chassisplatform via a second link; wherein the combination linkage employs afirst coupling feature and a second coupling feature, each of the firstand the second coupling feature configured to operably couple the firstand second chassis platforms; wherein the first coupling featurecomprises an attachment configured to rotate about a turning axis, andthe second coupling feature comprises at least one of a fixed attachmentor an attachment configured to pivot about a pivot axis that issubstantially perpendicular to the turning axis, the turning axis beingdefined as an axis about which the first chassis platform or the secondchassis platform rotates during a change in a heading of the roboticlawn mower.
 2. The robotic lawn mower of claim 1, wherein the first linkcomprises the second coupling feature of the fixed attachment extendingthe combination linkage rearward from the first chassis platform along alongitudinal centerline of the robotic lawn mower, and wherein thesecond link comprises the first coupling feature.
 3. The robotic lawnmower of claim 2, wherein the second link further comprises the secondcoupling feature of the attachment configured to pivot about the pivotaxis that is substantially perpendicular to the turning axis.
 4. Therobotic lawn mower of claim 1, wherein the combination linkage comprisesa curved shape defining a C-shape or U-shape portion through whichwheels of the second wheel assembly are enabled to pass when the secondchassis platform turns about the turning axis.
 5. The robotic lawn mowerof claim 1, wherein the second coupling feature comprises the attachmentconfigured to pivot about the pivot axis; wherein the combinationlinkage further comprises a pivot arm configured rotate about theturning axis when the second chassis platform turns about the turningaxis, wherein the second link is disposed on the pivot arm.
 6. Therobotic lawn mower of claim 1, wherein the combination linkage isconfigured to enable a portion of a wheel of the second wheel assemblyto pass under the combination linkage when the second chassis platformturns about the turning axis.
 7. The robotic lawn mower of claim 1,wherein the combination linkage provides a limit to an amount ofrotation the second wheel assembly is enabled to achieve when the secondchassis platform turns about the turning axis.
 8. The robotic lawn mowerof claim 1, wherein the turning axis is defined at a turn assemblydisposed at the second chassis platform, and wherein the turn assemblycomprises a turning shaft forming a portion of the second link, theturning shaft being housed to enable rotation of the second chassisplatform about the turning axis and pivoting about the pivot axis. 9.The robotic lawn mower of claim 8, wherein the turn assembly comprises apivot bearing housing configured to house pivot bearings oriented toallow pivoting about the pivot axis +/−5 degrees and a turn bearinghousing configured to house turn bearings disposed along the turningshaft to support rotational movement of the turning shaft of 360degrees.
 10. The robotic lawn mower of claim 1, wherein a wheelbase ofthe first wheel assembly is wider than a wheelbase of the second wheelassembly.
 11. The robotic lawn mower of claim 1, further comprisingprocessing circuitry configured to employ steering control for therobotic lawn mower, wherein the first wheel assembly comprises at leasttwo wheels individually powered by corresponding drive motors of a firstset of drive motors, and the second wheel assembly comprises at leasttwo wheels individually powered by corresponding drive motors of asecond set of drive motors.
 12. The robotic lawn mower of claim 11,wherein an angle sensor is mounted proximate to the turning axis tomonitor a turning angle of the second chassis platform relative to thefirst chassis platform, the angle sensor providing informationindicative of the turning angle to the processing circuitry to enablethe processing circuitry to employ the steering control based on theturning angle.
 13. The robotic lawn mower of claim 12, wherein theprocessing circuitry is configured to employ the steering control byindividually controlling a turning motor configured to control theturning angle responsive to input from the angle sensor.
 14. The roboticlawn mower of claim 11, wherein the processing circuitry is configuredto employ the steering control by individually controlling speed ordirection of driving each respective wheel of the first and second wheelassemblies.
 15. The robotic lawn mower of claim 1, comprising processingcircuitry configured to employ steering control for the robotic lawnmower; and an angle sensor mounted proximate to the turning axis tomonitor a turning angle of the second chassis platform relative to thefirst chassis platform, the angle sensor providing informationindicative of the turning angle to the processing circuitry to enablethe processing circuitry to employ the steering control based on theturning angle.
 16. The robotic lawn mower of claim 1, comprisingprocessing circuitry configured to employ steering control for therobotic lawn mower, wherein the processing circuitry is configured tomonitor a turning angle formed between the first chassis platform andthe second chassis platform and monitor an inclination of the roboticlawn mower to control the turning angle at least in part based on theinclination.
 17. The robotic lawn mower of claim 16, wherein theprocessing circuitry is configured to limit the turning angle responsiveto the inclination being greater than a predetermined amount.
 18. Arobotic vehicle comprising: a first chassis platform comprising a firstwheel assembly; a second chassis platform comprising a second wheelassembly, the first and second chassis platforms being spaced apart fromeach other; and a combination linkage operably coupling the first andsecond chassis platforms, wherein the combination linkage is operablycoupled to the first chassis platform via a first link and is operablycoupled to the second chassis platform via a second link, and whereinthe combination linkage employs at least two different coupling featuresto operably couple the first and second chassis platforms, the at leasttwo different coupling features comprising at least any two among afixed attachment, an attachment that enables rotation about a turningaxis, and an attachment that enables pivoting about a pivot axis that issubstantially perpendicular to the turning axis, wherein the combinationlinkage is configured to be under a portion of the combination linkagewhen the second chassis platform turns about the turning axis.
 19. Arobotic vehicle comprising: a first chassis platform comprising a firstwheel assembly; a second chassis platform comprising a second wheelassembly, the first and second chassis platforms being spaced apart fromeach other; and a combination linkage operably coupling the first andsecond chassis platforms, wherein the combination linkage is operablycoupled to the first chassis platform via a first link and is operablycoupled to the second chassis platform via a second link, and whereinthe combination linkage employs at least two different coupling featuresto operably couple the first and second chassis platforms, the at leasttwo different coupling features comprising at least any two among afixed attachment, an attachment that enables rotation about a turningaxis, and an attachment that enables pivoting about a pivot axis that issubstantially perpendicular to the turning axis, wherein the combinationlinkage is configured to enable a wheel of the second wheel assembly topass between the first and second chassis platforms when the secondchassis platform turns about the turning axis.